The present invention relates to a printing technology using a print head having multiple nozzles.
In recent years, ink jet printers that discharge ink from a head are widely used as computer output devices. Ink jet printers employ a print head having multiple nozzles for each ink.
One printing mode is established whereby sub-scan feed amounts and the number of nozzles used is controlled during printing with the printer. In such cases, there is some constraint in terms of sub-scanning feed amounts and number of nozzles used in order to perform recording at pixel positions on the printing medium without unnecessary duplications or omissions.
In this connection, it is desirable that as many of the mounted nozzles as possible are used in the execution of printing in order to improve printing speed. Towards this end, numerous different values for the sub-scan feed amount are used in combination in the technology described in JP-A-1998-278247 disclosed by the applicant of this application. In addition, this document also describes an xe2x80x9coverlap modexe2x80x9d in which recording of each main scan line is completed in two or more main scans. With overlap mode in which recording on each main scan line is completed in two main scans, the respective main scan lines are each scanned with two different nozzles.
However, with previous overlap mode, there has been the problem that there are restricted combinations of nozzles that carry out recording of a single main scan line. For example, main scan lines that are recorded using nozzle #1 are always recorded with nozzle #25, and main scan lines that are recorded using nozzle #2 are always recorded with nozzle #26. The number of nozzle combinations is thus restricted to one.
Because the number of combinations of nozzles used for recording a single main scan line is restricted to one, striated regions of image quality degradation referred to as xe2x80x9cbandingxe2x80x9d appears in the main scan lines. For example, due to manufacture differences in nozzles #1 and #25 that perform recording of the same main scan line, there are cases where dots are recorded at shifted positions in the same direction along the sub-scanning direction relative to the theoretical position (intended position). In such cases, a gap (specifically, banding) arises between a main scan line and its adjacent main scan line, resulting in image degradation.
This invention was developed in order to solve the above problems with conventional technologies, and has an object of offering a technology for mitigating image degradation in overlap mode.
In order to solve at least some of the problems described above, the present invention carries out printing on a printing medium during main scanning using a printing device which comprises a print head having one or more nozzle arrays each including a plurality of nozzles for forming dots of same color. The plurality of nozzles for forming dots of the same color have a constant nozzle pitch kxc3x97D in the sub-scan direction, where k is an integer of 2or greater and D is a dot pitch that corresponds to a printing resolution in the sub-scan direction. Each main scan line is scanned S times, where S is an integer of 2 or greater, using different nozzles. A combination of different values is used as feed amounts for Sxc3x97k sub-scans. When the feed amounts for the Sxc3x97k sub-scans are divided into S groups each containing k feed amounts for consecutive k sub-scans, a sequence of sub-scan feed amounts in at least one of the S groups of sub-scans is different from sequences in the other groups.
In the present invention, because the sequences of the S groups of sub-scan feed amounts are not the same, combinations of nozzles for recording the same main scan line are not fixed to only one, and multiple combinations are used. This results in reduction of banding and mitigation of image quality degradation.
It is preferable that intermittent pixel positions at a ratio of 1 to S pixels on a main scan line are serviced for dot formation in each of S main scans performed on the main scan line, and all of the pixel positions on the main scan line are serviced for dot formation by the S main scans.
In this case, the banding caused by the configuration where the combinations of nozzles for recording the same main scan line are fixed to only one tends to be particularly noticeable. Consequently, the aforementioned effect is particularly remarkable in such cases.
It is preferable that a ratio of the largest and smallest values of the Sxc3x97k sub-scan feed amounts is set at about 4 or greater.
In this configuration, even if banding should occur for whatever reason, the banding occurrence period varies with the value of the sub-scan feed amount, and so banding is not readily seen. The image quality degradation is further reduced consequently.
When a offset F is defined as a remainder obtained by dividing a cumulative value of sub-scan feed amounts by the integer k, a sequence of the offset F for at least one of the S groups of sub-scan feed amounts may be different from sequences for the other groups.
The offset F sequence is related very strongly to cumulative error occurring in the sub-scan feed, and using different offset F sequences tends to decrease cumulative error in the sub-scan feed, allowing mitigation of banding.
It is preferable that the sequence of the offset F for each group of sub-scan feed amounts is reversed from the sequence of the offset F for adjacent groups.
In this configuration, it is possible to additionally decrease the cumulative error in the sub-scan feed, thus making it possible to additionally reducing banding.
The effect of the above configuration related to the offset F sequence is particularly remarkable when dots are formed with a print head using pigment ink.
The present invention can be realized in various configurations, such as a printing device and printing method, a computer program for implementing the functions of the device or method, a computer readable recording medium storing the computer program, and a data signal embodied in a carrier wave that includes the computer program.